Field of the Invention
The present invention relates to a method of producing a polyimide resin, a method of producing a polyimide coating, and a method of producing a polyamic acid solution. The present invention further relates to a polyimide coating resulting from the method of producing a polyimide coating. The present invention still further relates to a polyamic acid solution resulting from the method of producing a polyamic acid solution.
Related Art
Polyimide resin is excellent in heat resistance, mechanical strength, and insulation properties and has properties such as a lower dielectric constant and thus has been widely used as an insulating material or a protective material in electric or electronic parts such as various devices and electronic substrates including multilayer wiring substrates.
The polyimide resin is typically formed by heat-treatment at a high temperature of about 300° C. of a polyamic acid obtained by polymerizing a tetracarboxylic acid dianhydride component and a diamine component in a polar organic solvent such as N-methyl-2-pyrrolidone (NMP), and dimethylformamide (DMF).
For this reason, polyimide products used for electronic materials are often supplied as a solution of polyimide precursor like a polyamic acid. When producing electric or electronic parts, the solution of polyimide precursor is supplied to a site where an insulating material or a protective material is to be formed by a process such as coating or injection, then the solution of polyimide precursor is heat-treated at a high temperature of about 300° C. to thereby form the insulating material or the protective material.
In such a conventional method of forming the insulating material or the protective material composed of the polyimide resin from the polyimide precursor, there is a problem in that the method cannot be applied to heat-sensitive materials since heat-treatment at a high temperature is necessary. Although there is also a solution of polyimide precursor allowing formation of a polyimide resin by treating at a lower temperature of around 200° C. for example, when forming the polyimide resin at lower temperatures, there may also be a problem in that heat resistance and/or mechanical properties of the resulting polyimide resin degrade or dielectric constant thereof increases.
For this reason, a method for obtaining the polyimide resin with excellent properties even by heat-treating a polyimide precursor at a lower temperature has been investigated. Specifically, Patent Document 1 discloses in Examples a method of producing a polyimide resin through imidization at 150° C. of a polyamic acid obtained by polymerizing 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane and 3,3′,4,4′-diphenylether tetracarboxylic acid dianhydride in propyleneglycol monomethylether acetate, for example.    [Patent Document 1] Japanese Unexamined Patent Application, Publication No. 2012-021133